1. Field of the Invention
The present invention relates to a method of protection of a structure constructed on ground which has a high water permeability and easily liquefies, such as sandy ground, and particularly to a protection method which is suitable to prevent sinking or floating of the structure.
2. Description of the Prior Art
When a structure is constructed on ground which has a high water permeability and easily liquefies, liquefaction may occur as a result of an earthquake because of elevation of the pressure of excessive pore water in the ground. Accordingly, in the past disasters caused by sinking or floating of such structures frequently have occurred as a result of earthquakes.
As a countermeasure to solve such a problem, there are known a method of improving the ground, a method of forming a gravel drain and a method of lowering of a ground-water level. However, to employ these methods, various conditions of the ground and restrictions on long term maintenance and management of the structures would be required. Thus, these methods are not frequently adopted.
A structure for preventing ground from liquefaction is disclosed in Japanese Provisional Patent Publication No. 127823/1983. However, this structure inevitably is accompanied by the following problems when it is actually used. Namely, in such structure, a predetermined number of drain pillars are provided in the base ground to support the structure. The drain pillars each comprise a concrete pillar having water permeability. On the outer circumference of the concrete pillar is formed a wall having water permeability with materials such as gravel, fine stone and slag. By this arrangement, it is attempted to employ the drain pillars to prevent an increase of the pressure of excessive pore water in the ground. However, it is difficult to construct such drain pillars under the structure, and even if possible, such construction requires a substantially high cost. Moreover, in the above-mentioned structure where the drain pillars are formed under the structure, the structure is liable to be floated by the pressure of water which elevates in the drain pillars when the ground becomes liquefied.
3. Object of the Invention
The present invention has been accomplished in an attempt to solve the above problems of the prior art. Therefore, it is an object of the invention to provide a method which can protect a structure constructed on ground which easily liquefies, which can prevent sinking or floating of the structure, and which can be achieved by a constructional operation that can be done easily and at low cost.